Roberts is perfectly knowledgeable here. He correctly notes that:
1. The "collective rights" versus "individual rights" argument was raised, and
2. The court sidestepped this issue, ruling instead on the question of whether a sawed-off shotgun was a type of weapon that fell within the scope of the Second Amendment. (As others have noted, they got this question wrong because Miller's side did not present any evidence, presumably because Miller had shuffled off this mortal coil before the case reached the Supreme Court.)
From this, we learn that Roberts understands that gun-control arguments asserting that "Miller is a precedent establishing the 'collective right' doctrine" are worthless jaw-flapping.
As others have noted, they got this question wrong because Miller's side did not present any evidence, presumably because Miller had shuffled off this mortal coil before the case reached the Supreme Court
miller's side presented evidence at district court level and won. it was declared that NFA was unconstitutional.
if you're interested in the district court case info here..
http://www.rkba.org/research/miller/Miller.html
Here we disagree completely. The court discussed "who is the Militia" and found no reason to exclude Miller. They could have refused to consider the case on "standing" which I believe is one of the first tests that a case must pass.
The court will refuse to hear cases from parties which lack standing because they do not wish to make rulings based on the circumstances of parties who are not affected by their decisions. The prosecutors who appealed the lower court decision could have counseled the Supreme Court to deny cert on standing grounds, but I see no indication that they did so.